body {
  margin: 0;
  display: flex;
  // 该属性是以下两个 CSS 属性的简写：aligh-items和justify-items
  place-items: center;
  min-width: 320px;
  min-height: 100vh;
  background-image: url('/images/map_bg.png');
}

#app {
  width: 100%;
  height: 100vh;
  margin: 0 auto;
}

ul {
  list-style: none;
}